The poinsettia (Euphorbia pulcherrima Willd. ex Ketsch) has become the most important Christmas flowering potted plat in the United States and Europe. The original introduction into the United States was in 1825 by the U.S. ambassador in Mexico, where it is native species.
The Ecke firm (Encinitas, Calif.) has been intimately associated with the commercial production of poinsettia stock plants since 1919. Until 1965, field grown dormant woody plants were shipped through the United States and the world. Since 1965, softwood vegetative cuttings (unrooted, callused or rooted) have been used to develop stock plants. Cuttings from Ecke's poinsettias are shipped to other greenhouse firms who produce vegetative cuttings for their own use or for sale to their grower customers. These vegetative cuttings are rooted, grown for various time spans and eventually "flower". In the northern hemisphere, flowering occurs under naturally shortening day lengths in the early fall, or under artificially shortened days at any time of the year. The true flowe is composed of numerous small cuplike structures, botanically known as cyathia. The showy bracts, which may be of red to cream-white in color, surround these cyathia and together form the inflorencense. These colorful bracts are botanically modified leaves.
Presently the Ecke firm has over 30 patented cultivars. These cultivars can be divided into those which are free branching or those which are restricted in their branching habit. The main difference is the propensity of shoots to elongate at the lower nodes. Restricted branching cultivars exhibit strong apical dominance as only a few (1 to 3) axillary shoots grow after the terminal growing point has been removed (pinched). Free branching cultivars form many axillary shoots depending on the number of nodes that remain after pinching. Consequently, restricted branching cultivars produce fewer vegetative cuttings; and when such plants are placed under short days, restricted branching cultivars produce fewer inflorescences.